There is no "obvious" about it, unless you define "intelligent" in a rather narrow (albeit Turing-esque) way.

The suspicion is that they are good at predicting next-token and not much else. This is still a research topic at this point, from my reading.

You can't predict the next token in an arbitrary text unless you are highly intelligent and have a vast body of knowledge.

They're obviously intelligent in the way that we judge intelligence in humans: we pay attention to what they say. You ask them a question about an arbitrary subject, and they respond in the same way that an intelligent person would. If you don't consider that intelligence, then you have a fundamentally magical, unscientific view of what intelligence is.